Method For Increasing The Accuracy Of The Positioning Of A First Object Relative To A Second Object

ABSTRACT

A method is provided for increasing the accuracy of the positioning of a first object relative to a second object. The method overcomes the disadvantageous influence of thermal drift between a first and a second object during a positioning of a first object on a second object. The method finds applications in manufacturing, for example, in the manufacturing of semiconductor components. The method utilizes recognition of structures on the second object which have a minimum structure width. At a first instant, using one recognition procedure, the first object is positioned on the second object in a desired position. The relative displacement of the two objects is determined at the first instant and on at least one subsequent instant. A second recognition procedure may be used for this purpose. The second recognition procedure may have a resolution accuracy which is different than the resolution accuracy of the first resolution procedure. The second recognition procedure may be a pattern recognition method. The relative displacement determined at the second instant is used to correct the positioning of the first and second objects as necessary to maintain a desired position of the two objects.

BACKGROUND OF THE INVENTION

In many areas of technology it is necessary to position objects relativeto one another with high precision. This requirement also exists in thefield of semiconductor technology, for example, during the testing ofsemiconductor components, which may be fabricated on semiconductorwafers. A plurality of semiconductor components of identicalconfiguration are generally situated on a semiconductor wafer. In thiscase, so-called probers are used for testing the semiconductorcomponents. For this purpose, contact pads are arranged at differentlocations in the semiconductor components (at the same location for eachsemiconductor component on the semiconductor wafer). During the testingwith the probers, contact is made with the contact pads by the tips ofcontact-making needles in the probers.

By means of such contact-making, an electrical contact with thesemiconductor component is produced, on the one hand to apply specificsignals to the semiconductor component and on the other hand to measurethe reaction to said signals.

According to setting methods in the prior art, the positioning ofcontact-making needle tips of a prober (referred to as a first object)relative to contact pads on the semiconductor component (referred to asthe second object) is performed under optical or visual control. In suchmethods, the semiconductor component is observed visually from above bymeans of a microscope and the prober needle tips are then positionedonto corresponding contact pads under visual observation. If the contactneedles happen to be set or positioned such that they lie on the contactpads of the semiconductor component, the setting operation is ended.

In some probers, it is also possible to mount the contact needles with acorresponding setting on a so-called needle card. A specific needle cardis used for each type of a semiconductor component. In such cases it isthen necessary to bring a further semiconductor component to be testedbelow the set contact-making needles so that the contact-making needlesagain make contact with the contact pads. If this has been done, thenext test operation can be performed.

The positioning of each semiconductor component below a structure ofcontact needles may be done manually under visual observation usingmanual probers commonly known in the prior art. Automatic probers alsoare known. In the case of automatic probers, it may be possible for eachsemiconductor component to be brought automatically below the structureof contact-making needles if the distances or orientation of the needlesand the semiconductor component is known (e.g., a rotation angle φ areknown). In this case, the displacement of the semiconductor waferrequired in order to perform an exact positioning may be calculated.

The visual or optical observation required for placing the needle tipson the contact pads may be performed by means of automatic imagerecognition systems. In this case, a pattern recognition is performed onor by an image of an observed region of the semiconductor component. Theimage may be recorded by a video camera, a CCD linear array or matrix orother image recording devices at a first instant. On account of thesurface structure of the semiconductor component, the latter has apattern. This pattern is significant for the component. If a furtheridentical component is now to be tested, the latter then exhibits thesame pattern. From the positional difference between the two patterns,the pattern recognition system can then determine geometrical correctionvalues required to allow the semiconductor component that is currentlyto be tested to be positioned precisely below the needle structure bymeans of a positioning device.

In the context of the increasing miniaturization of the structures onthe semiconductor components, considerable requirements or demands aremade for the proper positioning of the semiconductor component withrespect to the tips of the contact-making needles. The small widths ofthe miniaturized structures may be of the order of the wavelength of thelight making it difficult or impossible to visually or optically resolvethem to a sufficient extent. Thus, complex AFM probers, which operateaccording to the principle of atomic force microscopy (AFM), may be usedfor making contact with semiconductor component structures down in therange of 100 nm width. In this case, a contact-making needle is moved ata small distance above the surface of the semiconductor component, inparticular in the region in which the contact pad is situated. As aresult of the movement, the topography image of the region of thesemiconductor surface is scanned on account of an interaction forceoccurring between the contact needle and the semiconductor surface. Theexact position of the contact pad is may thus determined without theneed for a visual observation.

The contact-making needle is referred to as a cantilever in the case ofAFM probers. A piezo-drive is available for moving the cantilever, bymeans of which the cantilever executes a scan movement in order toobtain an image of the surface situated underneath, a scan. When the AFMprober is used, at a first instant, the region where contact issubsequently made is scanned by means of the cantilever. Once the scanis present, the tip of the cantilever is brought to the desired positiondetermined and brought into contact at a second instant.

What is problematic in this case is that the semiconductor wafer andcantilever are exposed to thermal influences. This leads to a thermaldrift in the time period between the first and second instants, i.e.,expressed generally, a relative displacement arises between the firstand second objects. In particular, this phenomenon occurs during thetesting of semiconductor components under thermally controlledconditions. A so-called thermo-chuck is used in this case, which, on theone hand, fixedly clamps the semiconductor wafer during the testoperation and, on the other hand, sets a desired temperature in a higheror lower temperature range in comparison with room temperature. Thetemperature alteration of the semiconductor wafer, for example onaccount of the thermal radiation, also influences the drive of thecantilever, as a result of which the drift occurs, which can no longerbe disregarded in particular in the case of the small structure widthssince, when making contact, the drift means that the cantilever nolonger meets the position which was previously determined during thescan operation.

As is rapidly apparent, even thermostatic regulation of the surroundingscannot provide a remedy here since the drift is generated by the methoditself. This problem area may also occur in other fields of application,in particular in the field of semiconductor technology, for exampleduring bonding operations. Therefore, as a general proposition, athermal drift or other drift between two objects can be problematic.

An object of the present invention is to prevent the disadvantageousinfluence of a thermal drift or other drift between a first and a secondobject during a positioning of a first object on a second object.

SUMMARY OF THE INVENTION

In accordance with the principles of the invention, a method forincreasing the accuracy of the positioning of a first object relative toa second object is provided. The method may find particular applicationsin the production or manufacturing of semiconductor components. Themethod utilizes a recognition of structures on the second object, whichhave a minimum structure width, for positioning the first object. In themethod at a first instant, the position of the first object relative toa second object is determined by use of a first recognition method orprocedure which has a resolution accuracy which is higher than theminimum structure width. The first object is then at a second instantpositioned at a desired position on the second object. Either the firstor the second object, or both, may be movable by means of a positioningdevice. Images of an observation region that encompasses at least thefirst object and the desired position are acquired during the method.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature, and various advantageswill be more apparent from the following detailed description and theaccompanying drawings, wherein like reference characters represent likeelements throughout, and in which:

FIG. 1 is a schematic representation of an image of an observationregion at a first instant in the process of placing a first object on asecond object, in accordance with the principles of the presentinvention; and

FIG. 2 is a schematic representation of an image of an observationregion at a second instant in the process of placing a first object on asecond object, in accordance with the principles of the presentinvention.

The following is a list of reference symbols used in the FIGS. 1 and 2:

LIST OF REFERENCE SYMBOLS

-   1 Semiconductor component-   2 Cantilever-   3 Contact pad-   4 Tip of the cantilever-   5 Observation region-   6 Structural element

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for overcoming the influence ofa thermal drift or other drift between a first and a second objectduring a positioning of a first object on a second object.

The inventive method overcomes the influence of thermal or other driftbetween the two objects by virtue of the fact that in the method, beforeor at a second instant, by means of a second recognition method, arelative displacement of the first object with respect to the secondobject is determined with regard to a first instant, but at least withrespect to the temporal proximity thereof, and the position of thesecond object is corrected during the positioning on the second objectby means of correction values which correspond to the relativedisplacement determined.

This method eliminates any temperature drift which may occur between thefirst instant and the second instant by ascertaining and correcting forthe relative displacement of the two objects between the first andsecond instants.

A favorable embodiment of the method provides for a pattern recognitionmethod to be used as the second recognition method. Pattern recognitionmethods record images of the observation region and acquire patternscontained in said images. By comparing two identical patterns which aredisplaced or rotated relative to one another in the imaging, it ispossible to determine the coordinate differences of each pixel of thetwo patterns. Computer-aided calculation of the positional displacementof the two patterns with respect to one another is thus possible.According to the invention, a pattern recognition method may now besuperimposed on the controlled positioning of the first object on thesecond object, thereby enabling the positional correction.

Since the pattern recognition methods recognize patterns which need notnecessarily represent sharp images, it is possible that the resolutionaccuracy of the pattern recognition method is lower (i.e. less fine)than the minimum structure width. As a result, the method according tothe invention can be realized very simply and cost-effectively.

Although it is possible, in principle, to carry out the secondrecognition method with a resolution accuracy which corresponds to or iseven greater (i.e., finer) than the minimum structure width, it is alsopossible to use a method which makes has less stringent requirements ofthe resolution accuracy. By way of example, it is possible to usescanning electron microscopes for the second recognition method in thecases of small structure widths in semiconductor technology that lie inthe wavelength range of the light. These scanning electron microscopeswould then sharply image the observation region. However, this sharpimaging would represent a pattern for a pattern recognition system inexactly the same way as the image of an optical microscope which wouldinevitably be unsharp on account of the proximity to the wavelength ofthe light. However, since the unsharpness does not adversely influencethe characteristic of a pattern (in contrast to an image), the patternrecognition method can thus operate in the light range, i.e.—in thisexample—with a lower resolution accuracy than the minimum structurewidth.

A particularly preferred embodiment of the method according theinvention may feature one or more of the following steps:

-   -   a step wherein the positioning device is brought into a basic        position x₀, y₀, φ₀ at the first instant T₀;    -   a step wherein in temporal proximity to the first instant T₀,        while the positioning device is situated in the basic position        x₀, y₀, φ₀, the pattern recognition method is used to acquire a        first image pattern from the observation region, which        encompasses at least the second object;    -   a step wherein in temporal proximity to the first instant T₀,        while the positioning device is situated in the basic position        x₀, y₀, φ₀, the pattern recognition method is used to acquire a        second image pattern from the observation region, which        encompasses at least the first object;    -   a step wherein the positioning apparatus is brought into the        basic position x₀, y₀, φ₀ before the second instant, the pattern        recognition method is used to acquire a third image pattern from        the observation region, which encompasses at least the second        object, and the pattern recognition method is used to acquire a        fourth image pattern from the observation region, which        encompasses at least the first object,    -   step wherein, by means of the pattern recognition method, a        first pattern displacement of the first object is determined        from the first and third image patterns and a second pattern        displacement is determined from the second and fourth image        patterns and the relative displacement is calculated from the        first and second pattern displacements; and    -   a step wherein the relative displacement calculated is used to        correct the desired position x₁, y₁, φ₁ of the positioning        device at the second instant.

The drift both of the first and of the second object with regard to thebasic position of the positioning device is determined by means of thisembodiment. The displacements of both objects are thus concomitantlyincluded or determined. From the difference between the respective twoimage patterns of the two objects it is possible to determine thedisplacement of the image patterns of the respective object and thusthat of the object itself. The relative displacement of the two objectswith respect to one another is then calculated from the displacements ofthe two objects, which becomes possible since the displacements of thetwo objects relate to a common basis, namely that of the basic position.

In an expedient manner, in a pattern recognition method, only in eachcase a common image pattern of the first and the second object isrecorded only in the basic position and in the desired position of thepositioning device. Since the pattern of the first object can be assumedto be known, the first pattern (or the second pattern if theconfiguration thereof is known) can then already be established from thecommon image pattern by means of the pattern recognition method. In thiscase, in one development of the method, the first image pattern isidentical to the second image pattern and/or the third image pattern isidentical to the fourth image pattern.

In a further variant of the method according to the invention, it isprovided that, after the second object, the relative displacements offurther objects are determined in an identical manner, from which,during the positioning of the further objects on the first object,correction values for correcting their desired positions are likewisedetermined. By way of example, if a plurality of contact needles orcantilevers are used for testing semiconductor components, it thusbecomes possible to correct all the drifts of all these objects.

In order to ensure that the first objects also actually remain in theobject desired position even if a drift occurs during the furtherprogression after the positioning of the first object on the secondobject, it is provided that, after the second instant, the determinationof the relative displacement with regard to the temporal proximity ofthe first instant is repeated and the position of the positioned firstobject on the second object is tracked such that the object desiredposition of the first object on the second object is complied with.

The invention will now be explained in more detail below on the basis ofan exemplary embodiment with reference to FIGS. 1 and 2 which showimages of an observation region at a first and second instant,respectively. The exemplary embodiment relates to the testing ofsemiconductor components 1 by means of a cantilever 2. Electricallyconductive connections (not specifically shown) are connected to thecantilever 2 and serve for applying test signals to the cantilever 2 andfor recording and forwarding reaction signals.

The cantilever is also connected to a positioning device (notspecifically shown). This positioning device is driven by apiezo-crystal which may execute only very small movements as seenmacroscopically but, as seen microscopically, whose movements can coverthe entire observation region. These movements can be executed veryrapidly by means of the piezo-crystal, so that the cantilever 2 can bescanned over the surface of the semiconductor component 1. The surfacemay thus be sensed by means of the principle of atomic force microscopy.Consequently, the position of a contact pad 3 onto which the tip 4 ofthe cantilever 2 can be positioned is also detected.

In the first position illustrated in FIG. 1, the sensing of the surfaceof the semiconductor component 1 has already been concluded. The tip 4thus “knows” its desired position on the contact pad 3.

The surface of the semiconductor component 1 is observed by means of aCCD camera over the observation region 5. The image of the observationregion shown in FIG. 1 and FIG. 2 is only figurative—since the minimumstructure width is ˜100 nm and the observation region is thereforeimaged in an unsharp or diffuse manner.

The image recorded by the CCD camera is processed further in the furtherprocess, as is demonstrated below. The image may also be displayed bymeans of a monitor for observing the operation.

Shortly before the scanning of the surface, the semiconductor wafer onwhich the semiconductor component 1 is situated (the semiconductorcomponent being shown only partially in FIG. 1 and FIG. 2,) may havebeen placed onto a thermo-chuck in order to carry out the testing underelevated temperatures. The semiconductor wafer is thus heated. Theheating process still persists at the first instant illustrated in FIG.1.

The heating process may give rise to a thermal drift, which becomesvisible in FIG. 2. FIG. 2 illustrates the observation region at thesecond instant. Dashed lines are used therein to illustrate the positionof the cantilever 2, of the contact pad 3 and of further structuralelements 6 from FIG. 1. It thus becomes possible to see the driftbetween the first and second instants in the form of a displacementΔy_(obj2), Δx_(obj2) of the contact pad 3 and of the structural elements6 in the x and y directions and a displacement Δy_(obj1) of thecantilever 2 in the y direction. The cantilever 2 has not experienced adrift in the x direction and neither the cantilever 2 nor thesemiconductor component 1 has experienced an angular displacement by therotation angle φ.

The exemplary embodiment is shown or described with only one cantilever2. In practice, however, a plurality of cantilevers may be used, themethod described below being employed correspondingly.

Directly after the scan described above, shortly after the first instantT₀, the basic position x₀, y₀, φ₀ is adopted by means of the positioningdevice. An image pattern is taken there and is compared with the imagepattern in the basic position x₀, y₀, φ₀ at the second instant T₁. Thepattern comparison is used to calculate the relative displacementbetween the semiconductor component 1 and the cantilever 2 from thedisplacements Δy′_(obj2), Δx′_(obj1) and Δy′_(obj1) of the imagepatterns, which correspond to the real displacements Δy_(obj2),Δx_(obj2) and Δy_(obj1) of the two objects. In the case of a setting ofthe desired position x₁, y₁, φ₁ for achieving an object desired positionin which the cantilever 2 lies above the contact pad 3, the desiredposition x₁, y₁, φ₁ is calculated correctively using the relativedisplacement.

Usually, in each case only one image pattern of the first and secondinstants are used for determining the displacements Δy′_(obj2),Δx′_(obj1) and Δy′_(obj1) of the image patterns. In this case, it isnecessary for the system to be taught the structure of the cantileverand the image pattern of the semiconductor component 1.

The methods for the one cantilever case and the multiple cantilever casemay be subdivided into a number of steps or substeps from a mathematicalview point.

The following steps may be carried out for one cantilever:

-   -   1. Learning of the cantilever models (as standard models, only        necessary in the case of a new type of cantilever or in the case        of another enlargement),    -   2. Calibration of the pattern recognition system with respect to        the positioning drive of the respective cantilever 2 (only in        the case of new installation or change in the enlargement),    -   3. Movement to the observation region 5,    -   4. Movement of the cantilever 2 out of the observation region 5,    -   5. Automatic learning of the structure of the semiconductor        component 1,    -   6. Scanning and movement into basic position,    -   7. Acquisition of the structure and cantilever coordinates,    -   8. Readjustment of the cantilever positions relative to the        structure coordinates with the aid of the positioning device,    -   9. Renewed acquisition of the structure and cantilever        coordinates and possible post-correction (successive        approximation),    -   10. Movement into object desired position.        The following steps may be carried out for a case with a        plurality of cantilevers:    -   1. Learning of the cantilever models (as standard models, only        necessary in the case of a new type of cantilever or in the case        of another enlargement),    -   2. Calibration of the pattern recognition system with respect to        the positioning drive of the respective cantilever 2 (only in        the case of new installation or change in the enlargement),    -   3. Movement to and learning of a specific test structure,    -   4. Constant movement of all the cantilever tips 4 on the test        structure and acquisition of the structure and cantilever        coordinates,    -   5. Scanning with a cantilever,    -   6. Movement into basic position of the respective contact        position (the contact position which corresponds to a        cantilever) and acquisition of the test structure and cantilever        coordinates,    -   7. Movement to the observation region 5,    -   8. Movement of the cantilever 2 out of the observation region 5,    -   9. Automatic learning of the structure of the semiconductor        component 1,    -   10. Scanning and movement into basic position,    -   11. Acquisition of the structure and cantilever coordinates,    -   12. Readjustment of the cantilever positions relative to the        structure coordinates with the aid of the positioning device,    -   13. Renewed acquisition of the structure and cantilever        coordinates and possible post-correction (successive        approximation),    -   14. Movement into object desired position.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. For example, the invention may be readily used inwireless data communication systems using any of the variety ofavailable or evolving wireless data communication protocols.

1. A method for increasing the accuracy of the positioning of a firstobject relative to a second object by utilizing a recognition ofstructures on the second object that have a minimum structure width, themethod comprising the steps of: (1) acquiring images of an observationregion that encompasses at least the first object and a desired positionon the second object; (2) at a first instant T₀, by means of a firstrecognition method having a resolution accuracy that is higher or betterthan the minimum structure width, determining the position of the firstobject relative to a second object; and (3) repositioning the firstobject relative the second object to the desired position at a secondinstant, wherein at least one of the first and the second objects aremovable using a positioning device, wherein before about the secondinstant, by means of a second recognition method, a relativedisplacement of the first object with respect to the second object isdetermined with respect to their positions at the first instant, andwherein step (3) further comprises correcting for the relativedisplacement of the first object with respect to the second object. 2.The method of claim 1 wherein a pattern recognition method is used asthe second recognition method.
 3. The method of claim 2 wherein theresolution accuracy of the pattern recognition method is lower or poorerthan about the minimum structure width.
 4. The method of claim 2,further comprising: bringing the positioning device to a basic positionx₀, y₀, φ₀ at about the first instant T₀, and further in temporalproximity to the first instant T₀ using the pattern recognition methodto acquire a first image pattern from the observation region thatencompasses at least a portion of the second object and a second imagepattern from the observation region that encompasses at least a portionof the first object; bringing the positioning device to a basic positionx₀, y₀, φ₀ before about the second instant, and further using thepattern recognition method to acquire a third image pattern from theobservation region that encompasses at least a portion of the secondobject, and a fourth image pattern from the observation region thatencompasses at least a portion of the first object; by means of thepattern recognition method, determining a first pattern displacementfrom the first and third image patterns and a second patterndisplacement from the second and fourth image patterns and furtherdetermining the relative displacement from the first and second patterndisplacements; and using the relative displacement to correct theposition x₀, y₀, φ₀ of the positioning device to a desired position atthe second instant.
 5. The method of claim 4 wherein at least one of thefirst image pattern and the third image pattern is respectivelyidentical the second image pattern and the fourth image pattern.
 6. Themethod of claim 1 further comprising, after the second object isprocessed, determining the relative displacements of the first objectand further objects that have minimum structure widths using steps thatare identical to steps (1)-(3) to correct the relative positions of thefurther objects and the first object.
 7. The method of claim 1 furthercomprising, after the second instant, repeating in time thedetermination of the relative displacement of the first and secondobjects so as to maintain a desired position of the first object on thesecond object.